1. Field of the Invention
The present disclosure relates to an oxide semiconductor thin film and a method of manufacturing a thin film transistor (TFT) using the same, and more particularly, to a semiconductor thin film comprising ZnO and a method of manufacturing a TFT using the same.
2. Description of the Related Art
Thin film transistors (TFTs) using a semiconductor thin film are applied in various fields, and are often used as active devices for flat panel displays. Specifically, oxide semiconductor films, particularly, semiconductor films comprising ZnO, for example an amorphous gallium-indium-zinc-oxide (GIZO) semiconductor film, can be processed at low temperatures and can be easily made on a large scale. Also, since the semiconductor film comprising ZnO has a high mobility, the ZnO-based semiconductor film has good electrical properties like a polycrystalline silicon film.
However, carrier concentration in the ZnO-based semiconductor film is sensitive to changes in oxygen concentration, and the physical and electrical properties of the ZnO-based semiconductor film are greatly affected by both thermal and chemical treatments. When a TFT comprising a ZnO-based semiconductor film is manufactured, the ZnO-based semiconductor film is exposed to high-energy plasma and is thus subject to plasma-induced damage and thermal damage, thereby increasing the carrier concentration. The abnormal increase in the carrier concentration shifts the threshold voltage of the ZnO-based TFT to a larger negative voltage, such that a large leakage current flows between a source electrode and a drain electrode even when the gate voltage is 0 V. The leakage current is a critical problem in cases where the ZnO-based TFT is a back channel etch (BCE) TFT in which a SiNx passivation layer is formed on both the source and the drain electrodes, and where the ZnO-based TFT is an etch stopper TFT in which a channel layer is protected by an etch stopper and both the source and the drain electrodes are formed by etching.
In short, the damage to the channel layer resulting in the shifting of the threshold voltage, is related to an increase in the carrier concentration in the channel layer. Accordingly, there is a demand for a method of manufacturing a ZnO-based TFT having good electrical properties by controlling the carrier concentration.